The invention relates to supporting substrates in a near vacuum or other low-pressure processing environments using thermally conductive as well as temperature-regulating chucks for transferring heat to or from the substrates.
Vacuum processing operations take place in vacuum chambers that provide near vacuum or other low-pressure environments for processing substrates. Chucks support the substrates within the processing chambers. Some such chucks merely provide a substrate support platform and rely on gravity to hold the substrates in place. Others actively secure the substrates with either mechanical or electrostatic clamps.
Some chucks are also involved with the processing of the substrates by producing electrical or magnetic fields or by regulating heat transfers to or from the substrates. Such electrical fields (e.g., bias) can be used to generate or enhance a plasma as well as to direct plasma ions impinging on the substrate. Such magnetic fields can be used to also influence the plasma or to magnetically orient films during plasma-assisted deposition or thermal anneals. Heat transfers are used to remove excess heat from the substrates produced by such processing operations or to provide a controlled amount of substrate heating for assisting such processing operations. Some operations are best performed at fixed substrate temperatures or at substrate temperatures that are adjusted throughout different stages of the operations. Plasma sputtering operations such as chemical-vapor deposition (CVD) and metal-organic chemical-vapor deposition (MOCVD) require active substrate heating, while other sputtering operations require active substrate cooling. During operations like thermal annealing, elevated temperatures actually accomplish the substrate processing.
However, controlling substrate temperatures in near vacuum or other low-pressure environments is quite difficult because heat does not transfer well between objects in such environments. For example, the conduction of heat between contiguous surfaces of a chuck body and the substrate in a low-pressure environment is slow and inefficient because actual contact on an atomic scale between the surfaces is limited to a small fraction of their common areas, and gaps that separate the remaining common areas of their surfaces prevent effective heat transfer by conduction.
Heating and cooling of substrates through radiational heat transfers are possible in low-pressure environments, particularly at elevated substrate and chuck temperatures, but radiational heat transfers are generally too slow to maintain substrates at desired processing temperatures. Below 500xc2x0 C., which includes most chuckbased fabrication processes, radiational heat transfers are too inefficient to regulate substrate processing temperatures.
Faster transfers are possible by pumping a gas, preferably an inert gas such as helium or argon or another gas such as nitrogen or hydrogen, between the chuck body and the substrate. Although still at much less than atmospheric pressure (e.g., 1 Torr to 20 Torr), the gas (referred to as xe2x80x9cbackside gasxe2x80x9d) sufficiently fills the small gaps between the chuck body and the substrate to support significant heat transfer through thermal conduction between them. A seal formed between the mounting surface of the chuck body and the substrate resists significant leakage of the gas into the rest of the processing chamber, which could disturb substrate processing operations.
U.S. Pat. No. 4,680,061 to Lamont, Jr. discloses chucks having heating or cooling elements for regulating substrate temperatures. One of the chucks has a ceramic heating element mounted in a cavity between a chuck body and a substrate. The heating element is mounted close to a back side of the substrate but not in contact. Argon gas is introduced into the cavity to promote heat exchanges between the heating element and the substrate. A raised rim of the chuck body on which the substrate is mounted contacts a peripheral portion of the substrate""s back side forming a seal that inhibits leakage of the gas out of the cavity.
Another of Lamont, Jr.""s chucks has a chuck body that functions as a heat sink with coolant channels for removing heat from the sink. A similar cavity is formed by a raised rim in the chuck body so that the remaining heat sink is positioned close but not in contact with the back side of a substrate. Argon gas is similarly trapped within the cavity by contact between the raised rim of the chuck and the back side of the substrate. Thus, the raised rim that supports the substrate also functions as a seal for inhibiting leakage of the gas into the rest of the processing chamber.
U.S. Pat. No. 4,949,783 to Lakios et al. also discloses a chuck using gas pressure against a back side of a substrate to promote substrate cooling. A similar cavity is formed in the chuck body and surrounded by a raised rim for contacting the back side of the substrate. However, instead of merely pumping backside gas into the cavity, Lakios et al. circulate the backside gas both into and out of the cavity by establishing a gas flow. Part of the heat transfer from the substrate is due to gas-conducted heat exchanges with the chuck body, and another part of the heat transfer is due to the removal of heated gas from the cavity.
The chucks of both Lamont, Jr. and Lakios et al. include raised rims on their chuck bodies that function as both mounting surfaces and seals. Mechanical clamps press the substrates against the raised rims of their chuck bodies to tighten the seals and to reduce leakage of backside gas into their processing chambers. Lakios et al. also use an O-ring seal next to their raised rim to provide an even tighter seal for further reducing leakage. However, such O-ring seals are normally not useable for elevated substrate-temperature processing (e.g., above 200xc2x0 C.) because of thermal limitations of elastomer seals.
The raised rims of the prior chucks separate conductive portions of the chuck body from the substrate, which reduces efficiency of heat transfers between them. Also, some leakage of substrate backside gas can occur through the raised rims, particularly through rims made to withstand elevated temperatures during substrate heating operations. Substrate back side surface roughness can also reduce the effectiveness of the raised rim seals and lead to excessive leakage of backside gas into the processing region of the processing chamber.
This invention in one or more of its embodiments improves chucks that use gas or other fluid as a medium for transferring heat to or from substrates in a vacuum processor by providing a two-stage sealing system that reduces leakage of the gas from between the chucks and the substrates into the processing region of the vacuum processor. A first sealing stage confines the gas between preferably contiguous first portions of the chucks and substrates for supporting transfers of heat. A second sealing stage collects gas escaping through the first sealing stage into an intermediate space between second portions of the chucks and substrates at a reduced pressure with respect to the pressure at which the gas is confined within the heat-transfer interface.
The processing region of the vacuum processor is a first pressure-regulatable space. The first sealing stage together with the first portions of the chuck and substrate forms a second pressure-regulatable space, and the second sealing stage together with the second portions of the chuck and substrate forms a third pressure-regulatable space. Pressure in the third pressure-regulatable space is reduced with respect to pressure in the second pressure-regulatable space to further inhibit leakage of gas from the second pressure-regulatable space into the first pressure-regulatable space.
One particular embodiment includes a chuck body having a mounting surface that supports the substrate for processing within the first pressure-regulatable space of the processing chamber. The mounting surface forms together with the substrate a second pressure-regulatable space for assisting transfers of heat between the chuck body and the substrate. A clamp presses the substrate against the mounting surface and forms together with the chuck body and the substrate a third pressure-regulatable space that extends beyond a periphery of the substrate between the first and second pressure-regulatable spaces.
The substrate includes a front surface (usually comprising devices in various stages of fabrication) exposed to pressure in the first pressure-regulatable space and a back surface exposed to pressure in the second pressure-regulatable space. The mounting surface contacts the back surface of the substrate for inhibiting flows of fluid (e.g., backside gas) between the second and third pressure-regulatable spaces. The clamp contacts the front surface of the substrate and the chuck body (or an extension of the chuck body) for inhibiting flows of fluid between the first and third pressure-regulatable spaces.
The mounting surface and the back surface of the substrate are preferably contiguous over most of their common overlapping areas to enhance transfers of heat between them. Channels in the mounting surface interrupt a central portion of the common area to circulate gas within the second pressure-regulatable space, while a surrounding portion of the common area remains uninterrupted to provide the first-stage seal.
A recess in the clamp or the chuck body provides an enclosed cavity or manifold for collecting gas within the third pressure-regulatable space. One second-stage seal joins the clamp to the front surface of the substrate, and another second-stage seal joins the clamp to the chuck body. One of the second-stage seals is preferably mounted from a flexible portion of the clamp to assure contact at both second-stage seals of the clamp as well as the first-stage seal between the mounting surface of the chuck body and the substrate.
Inlet and outlet conduits preferably provide a continuous flow of gas through the second pressure-regulatable space. Separately controlled outlet conduits can be used to remove gas from the third pressure-regulatable space for reducing the pressure in the third pressure-regulatable space with respect to the pressure in the second pressure-regulatable space and for minimizing substrate backside gas leakage into the processing portion of the processing chamber (i.e., the first pressure-regulatable space).
Another embodiment can be described as having first and second substrate mounting components for mounting a substrate for processing in a first pressure-regulatable space and for forming together with the substrate second and third pressure-regulatable spaces. The first substrate mounting component, which is in thermal communication with a temperature-regulating (e.g., heating or cooling) element, has a first-stage seal surrounding a central portion of the substrate for confining fluid (e.g., backside gas) within the second pressure-regulatable space. A second substrate mounting component, which is at least partially thermally isolated from the temperature-regulating element and the first substrate mounting component, has at least one second-stage seal surrounding the second pressure-regulatable space for confining fluid within the third pressure-regulatable space in substantial isolation from the first pressure-regulatable space. A control system reduces pressure in the third pressure-regulatable space with respect to pressure in the second pressure-regulatable space to inhibit leakage of fluid from the second pressure-regulatable space into the first pressure-regulatable space.
The first substrate mounting component can include a chuck body having a mounting surface that supports the substrate for processing within the first pressure-regulatable space of the processing chamber. The second substrate mounting component can take various forms including a mechanical clamp as described above or a peripheral support surrounding the chuck body. In the latter case, the mounting surface can be built up from alternating layers of electrically conductive and non-conductive films patterned as electrodes to form an electrostatic clamp for pressing the substrate against the chuck body as well as the peripheral support. A first second-stage seal joins the peripheral support to the back surface of the substrate, and a second second-stage seal joins the peripheral support to the chuck body or an extension of the chuck body. The second second-stage seal can join the peripheral support directly to a heat-conducting portion of the chuck body or indirectly through a thermal insulator. Particularly during heating operations, the peripheral support is preferably constructed to minimize transmissions of heat with either the substrate or the chuck body.
Since the second substrate mounting component (e.g., peripheral support) is interposed between the heat-conducting portion of the chuck body and the first second-stage seal, more options are available for regulating temperatures at the first second-stage seal. For example, the second substrate mounting component can function as a thermal insulator during heating operations to lower temperatures at the first second-stage seal. The area of the second substrate mounting component exposed to gas within the third pressure-regulatable space and the proximity of the second substrate mounting component to the heat-conducting portion of the chuck body are other design variables that can be used to regulate thermal conduction of the second substrate mounting component.